Presence Of Ultrasonic Vibrations Research Articles

The thermal effects of multi-walled carbon nanotube concentration on an ultrasonic vibrating finned tube heat exchanger

The present study experimentally investigates the effects of nanofluid concentration on forced convective heat transfer in an ultrasonic vibrating finned tube heat exchanger. A specific experimental setup is constructed to perform the tests, and Multi-Walled Carbon Nanotube (MWCN) is used as the medium fluid. A proper validation test, as well as an uncertainty analysis, is done to ensure the authenticity of the results. The effect of several parameters, including ambient temperature (30–40°C), the velocity of passing air (0.1-1 m/s), and also MWCNT concentration (0.1–0.5 wt%), have been investigated. Two scenarios with and without the presence of ultrasonic vibrations are studied in detail. It is revealed that increasing nanofluid concentration can positively emphasize the ultrasonic vibration's effect while the increase of ambient temperature and passing air velocity reduces the ultrasonic effect. In the lowest ambient temperature (30°C) and air velocity (0.1 m/s) of the current experiment, the outlet temperature heat transfer will increase by 19.18% in the presence of vibrations for an MWCNT concentration of 0.5 wt%. In the best condition, the heat transfer will enhance 80.52% by imposing ultrasonic vibration. This study may constitute a promising approach for taking advantage of both nanofluid and ultrasonic vibration.

Magnetic field and ultrasonic aided laser drilling effect on Ti6Al4V microstructural characteristics

ABSTRACT Today, the utilization of millisecond pulse laser drilling, despite the extensive applications in different fields, is accompanied by several limitations such as low penetration depth, high thickness of recast layer, and heat-affected zone. In order to overcome these limitations, different techniques such as applying magnetic field as well as utilizing ultrasonic vibrations have been proposed. Up to now, limited investigations have been conducted regarding the effect of simultaneous addition of magnetic field and ultrasonic vibration on microstructural characteristics; therefore, in this paper, the simultaneous effects of magnetic field (0.5 Tesla intensity) and ultrasonic vibrations (with the frequency of 28 kHz and amplitude of 15 μm) on the formed phases, recast layer and heat-affected zone thickness have been studied in laser drilling of Ti6Al4 V. According to the results, 23.53% and 6.31% reductions were obtained in diameter and depth of the drilled hole compared to conventional laser drilling, respectively. Moreover, the diameter of heat-affected zone, in the inlet of the drilled hole, was reduced by 30.33% in this hybrid process compared to conventional laser drilling. Besides, it was observed that the presence of ultrasonic vibrations prevents from the formation of acicular α structure in the recast region of Ti6Al4 V.

Experimental and numerical study on heat transfer enhancement using ultrasonic vibration in a double-pipe heat exchanger

Heat transfer enhancement of double-pipe heat exchanger in the presence of ultrasonic vibrations is experimentally and numerically studied. A novel experimental setup made of two concentric pipes is constructed and a bolted Langevin ultrasonic transducer is used for applying the ultrasonic vibrations to the inner pipe with a frequency of 26.7 kHz. The numerical simulation is carried out by OpenFOAM software to clarify the reason for heat transfer enhancement. The effects of hot and cold fluid flow rates and acoustic power on heat transfer and pressure drop are studied in this work. The performance of heat exchanger is investigated by comparing the overall heat transfer coefficient and pressure drop with and without the influence of ultrasonic vibrations. Results show that using ultrasonic vibration is more effective at low fluid flow rates. As a result, heat transfer enhances about 60% for both cold and hot fluid flow rates of 0.5 L/min, while heat transfer enhancement is equal to 20% for cold and hot fluid flow rates of 1 and 1.5 L/min, respectively, at the transmitted acoustic power of 120 W. Numerical results demonstrate that the cross-stream flows generated by propagation of ultrasonic waves into the cold fluid are responsible for heat transfer enhancement.

Investigating the Ultrasonic Assistance in the Tube Hydroforming Process

The purpose of introducing ultrasonic vibrations in the tube hydroforming process is to create more formability by obtaining a lower corner radius, improve thickness distribution of the wall and provide good tribological conditions at the tube and the die interface. Vibrations imposed on the die create alternating gaps which improve the formability in the tube hydroforming process in the presence of ultrasonic vibrations. Therefore, we attempted to understand the processing mechanism of the ultrasonic tube hydroforming in the square die using the finite element method. Abaqus software was used in these simulations and the die was considered as a deformable element.

Evaluation of local strain distribution in ultrasonic enhanced Al 6061-T6 friction stir weld nugget by EBSD analysis

Representative strain states in Al 6061-T6 friction stir weld nuggets prepared with and without ultrasonic vibration were evaluated using strain component data from electron backscattered diffraction analysis. Strain components of various weld nugget locations in final grain structures and approximate strain components of the similar locations at a pseudo-intermediate grain size were accessed by varying average grain size of locations during data processing. Net strain components at the pseudo-intermediate states were higher than those at the final grain structure. Variations in net strain components at each location were analyzed to elucidate grain structure evolution with and without the ultrasonic effect. Results revealed that strain component distributions varied from location to location. Net strain component at center location increased with depth while it decreased towards weld nugget extremities. The net strain components are slightly higher in the presence of ultrasonic vibrations. Relative effect of ultrasonic energy on grain structure evolution is interpreted based on specific strain component (SSC). In the presence of ultrasonic vibrations, SSC is high which causes higher strain dependent grain refinement and recrystallization is most affected by strain. When SSC is low, additional factors control recrystallization. Position of ultrasonic factor reflects the ultrasonic effect.

Investigation of ultrasonic vibration effects on the microstructure and hardness of aluminum alloy 2024 tube spinning parts

Tube spinning process, also known as flow forming, is one of the manufacturing methods in production of seamless tubes. During the tube spinning process, the workpiece was excited by ultrasonic vibrations. The authors’ last research was focused on variation of forming forces and surface effects of tube spinning parts under ultrasonic vibrations. In the present study, the effects of ultrasonic vibrations on mechanical and metallurgical properties of AA 2024 workpieces were investigated. In fact, different characteristics of the workpiece in the presence and absence of ultrasonic vibrations were evaluated. The results of microstructure and microhardness tests revealed that in the presence of ultrasonic vibrations, precipitate formation was reduced. Also, precipitate shape and distribution through microstructure, particularly near the outer surface up to 2 mm depth, was changed. In addition, applying ultrasonic vibrations not only increased the hardness and the depth of hardened layers but also improved the uniformity of hardness profile across the thickness.

The effect of friction reduction in presence of ultrasonic vibrations and its relevance to travelling wave ultrasonic motors

In many ultrasonic applications frictional effects play an important role (e.g. ultrasonic machining, ultrasonic motors). For optimising the applications in terms of quality, efficiency and lifetime it is important to understand the frictional coupling of the vibrating and the non-vibrating part. This contribution is devoted to give an explanation for the reduction of friction forces which is often observed when ultrasonic vibrations are superimposed to macroscopic motions. Usually adopted coefficients of friction are used for modelling such conditions suggesting special frictional mechanisms for high frequency oscillations, whereas the present paper shows that Coulomb's friction law provides a very good description of the observed phenomena if the kinematics of the system is taken into account. Two systems are investigated. In the first system the ultrasonic and macroscopic movements are parallel and in the second they are perpendicular to each other but also within the plane of contact. Both systems were investigated analytically and experimentally using a specially designed test rig. The measurements confirmed the analytically derived equations and therefore the validity of Coulomb's friction law even for ultrasonic conditions.

Growth striations in Bi-Sb alloy single crystals pulled in the presence of ultrasonic vibrations

Single crystals of Bi-Sb alloys were grown by a modified Czochralski method. Ultrasonic vibrations at a frequency of 0.65, 2.5 or 5 MHz were introduced into the melt, and their effect on crystal growth was investigated by observing striations in the crystals. A strong decrease in density of the growth striations in crystals pulled with ultrasonic vibrations was found.

Changes of the growth morphology in insb crystals pulled under the presence of ultrasonic vibrations

AbstractIn the Czochralski method, the effect of ultrasonic vibrations on the growth of InSb single crystals was investigated by observing the growth morphology. Remarkable changes which ultrasonic vibrations brought about were: (1) the crystal diameter, (2) the width of the facet region and (3) the inclined angle of non‐facet interfaces near the facet region for the (111) plane. After introducing vibrations, the crystal diameter decreased smoothly with growth time. However, both the facet width and the inclined angle reached each minimum value after 5 to 7 min regardless of the magnitude of vibrational output powers from 30 to 90 W, and they were in roughly proportional relation with each other. The change rates of crystal diameter and of facet width increased with vibrational powers. The decrease of crystal diameter was known to result from the rise of the melt temperature, which was brought by both the mixture of the melt and the thermal energy transformation due to ultrasonic vibrations. The change of facet width depended upon the melt flow itself in addition to the temperature rise.

Line shape of the mössbauer line in the presence of ultrasonic vibrations with decaying amplitudes: Kornfeld, G., Physical Review, Vol 177, No 2 (10 January 1969) pp 494–501 (1410)

Line shape of the mössbauer line in the presence of ultrasonic vibrations with decaying amplitudes: Kornfeld, G., Physical Review, Vol 177, No 2 (10 January 1969) pp 494–501 (1410)

Line Shape of the Mössbauer Line in the Presence of Ultrasonic Vibrations with Decaying Amplitudes

Line Shape of the Mössbauer Line in the Presence of Ultrasonic Vibrations with Decaying Amplitudes